Low Impact Development

Development and property management techniques that minimize water pollution impacts off-site are called Low Impact Development, or LID. There is some very clever engineering involved in some cases, but for the most part this is not rocket science. Sources on the property should be minimized, but recognizing limits on residential properties, the vehicle for off-site transport, runoff, is restricted. The idea is to limit impervious surfaces and collect as much runoff as possible for infiltration or detention on the property. The focus is on actions at the individual property level, rather than some larger downstream facility to hold greater quantities of runoff long enough to allow it to be purified by natural or engineered means.

Typical techniques include bioretention (rain gardens), porous pavement, grass swales, and green roofs. These techniques can work in almost any climate; having a cold winter is not really a deterrent. Sizing is important, but the most critical limitation tends to be soil type. Turning runoff into ground water provides excellent treatment and has not resulted in extensive ground water contamination, although each case must be considered individually. However, not all soils are conducive to receiving as much runoff as can be derived from roofs, driveways and packed lawn areas. Engineering in such cases is most critical and may be challenging. Where runoff cannot be percolated, it may be detained and purified by various means before being released to a stream or lake.

There is a fair amount of literature out there that explains the techniques and reviews results, but one does have to do a lot of reading to get up to speed. One accessible reference that is helpful and has an extensive reference list is Ahiablame, L.M., Engel, B.A. & Chaubey, I. Water Air Soil Pollut (2012) 223: 4253. doi:10.1007/s11270-012-1189-2. Another publication, free from the USEPA, is Reducing Stormwater Costs Through Low Impact Development Strategies and Practices. The key limitation to wider application has been insufficient documentation of results, which is a difficult problem. One can demonstrate success at the individual property level, but showing positive impacts on an entire lake ecosystem is challenging, since the extent of application has to be very high. Another troublesome aspect is that removal of phosphorus, probably the most important nutrient entering our lakes, is not especially high; one cannot completely counter the impact of development on a lake with LID. The good news is that there is very little downside; anything homeowners can do to limit contaminated runoff from leaving the home site will benefit the lake, and application of LID techniques is less expensive than alternative measures.

Reducing Stormwater Costs through Low Impact Development